In my Ruby on Rails side project, I’ve been using the Filterrific gem for filtering. And it’s been terrific. But then I had to add a new filter and I just couldn’t figure out how to get it to work. I searched online for a few days and found little things that helped me in the end but nothing that fit just right so I’m writing about what I came up with in the event it might help others. It’s probably not the best solution but it works.

Models

I have three models with the following relationships:

class Issue < ActiveRecord::Base
  has_many :votes
  ...
end

class User < ActiveRecord::Base
  has_many :votes
  ...
end

class Vote < ActiveRecord::Base
  belongs_to :issue
  belongs_to :user
end

Process

I didn’t have much trouble writing the scope to filter by given votes for the current user. So you could find issues for which you voted with a yes or a no or both. But you couldn’t find issues you haven’t voted on yet. Here’s the original scope:

I was having trouble figuring out how to get the issues which didn’t have votes for the current user. I could do it with SQL:

But I really didn’t want to use SQL. And I had to combine with the existing where statement with an “OR”. I looked back at the Filterrific documentation again and saw Jo Hund had made a major upgrade to version 2.0 since I started using the gem. He also added more scope examples to the documentation. Great! I upgraded my gem and updated my code first. Some of his examples use Arel which I didn’t know much about. I’m still kind of new to Rails. But it looked interesting.

Final Result

I’ll cut to the chase and show what I finally came up with after a LOT of trial and error. But I kind of doubt this code is very efficient. And I also have several questions about it outlined below.

Questions

Question 1

I was able to come up with the no_vote_relation on line 35. But then I had to redo my where statement in my original vote types scope above to be an arel relation. This took a little longer and the vote_types_relation on line 29 works but it seems much more complicated. And I didn’t think I should need to use an in for it. But it was the only thing I could come up with to get the join to work. Anyone have any suggestions for this? Or is it fine?

Question 2

Both the no_vote_relation and the vote_types_relation have a large portion of code that is identical between the two. So I tried to DRY out the code. See commented line 24. But when I tried to use that issue_vote_join_relation inside the other two (see commented lines 28 and 34), the scope method would get called about four times. That seems extremely bizarre to me. There’s probably a reasonable explanation. Let me know if you know what it is.

Question 3

The simple where call at the end of the method works. But based on one of the Filterrific examples, I thought I needed to do something like this:

where(
  Issue \
    .where(final_rel)
)

But that didn’t work. Just using the where by itself was a complete guess. It just happened to work. I still don’t understand going between arel relation and ActiveRecord::Relation. I need to do more research into this. If you have references or explanations, let me know.

Conclusion

I hope this helps someone out there working on complex or queries with a join in a scope method since I couldn’t find anything similar online. If you can answer any of my questions above or have anything to say about the efficiency of the code, please comment below. Thanks!